1. Field of the Invention
The present invention relates to a decentered optical system and a projecting apparatus employing the same which are ideally used for a liquid crystal projector or the like and which successfully correct distortion, trapezoidal distortion, the fall of an image surface, etc. by properly setting the lens configuration of the decentered optical system so as to provide a projection image having good optical characteristics when, for example, magnifying and projecting an original projected image, which is displayed on a liquid crystal display device or the like, onto a screen from a slant direction.
2. Description of Related Art
Hitherto, a variety of projecting apparatuses or liquid crystal projectors for projecting an image, namely, a projection image original picture, which is displayed on a liquid crystal display device, onto a screen have been proposed. FIG. 12 is a schematic diagram illustrating an oblique projection type projecting apparatus which projects a projection image original picture LP onto a screen surface S in a slant direction through a projection lens 7 for the purpose of observation.
The projecting apparatus shown in the drawing makes use of a screen shift in which the center LPa of the projection image original picture LP is shifted downward with respect to an optical axis 8 of a projection lens assembly 7 in order to prevent the projection image from being distorted when projecting the projection image original picture LP on a screen S.
There is a related art disclosed in Japanese Unexamined Patent Publication No. 5-273460.
In the projecting apparatus shown in FIG. 12, the projection image original picture LP is shifted downward in relation to the optical axis 8 of the projection lens assembly 7. For this reason, it is required to make an image circle, i.e. an effective screen, of the projection lens 7 assembly considerably larger than the diagonal dimension of the projection image original picture. This has been leading to the tendency toward larger size and more complexity of the projection lens assembly 7.